Nitrogen oxides in exhaust gases discharged from power plants, various kinds of plants and factories, automobiles and the like are causative substances of photochemical smog and acid rain. The exhaust gas denitrification process by selective catalytic reduction with ammonia (NH3) etc. as a reducing agent is widely used in thermal power plants and the like in order to effectively remove nitrogen oxides.
As catalysts, titanium-oxide (TiO2)-base catalysts are used which include vanadium (V), molybdenum (Mo), tungsten (W) and the like as active constituents. In particular, catalysts containing vanadium as one of active constituents have become mainflow of present denitrification catalysts because these catalysts not only have high activity, but also less deteriorates due to impurities contained in exhaust gases and hence can be used at lower temperatures (for example, Patent Literature 1).
Catalyst structures are shaped in such structures as a honeycomb structure and a plate-like structure and various methods of manufacturing a catalyst structure have been proposed. For example, there have been proposed catalyst structures in which a net-like object made of a thin metal sheet formed into a metal lath, and a woven cloth or nonwoven cloth of ceramic fiber are used as a base, and plate-like catalyst structures, each of which is obtained by applying and pressure bonding a catalyst constituent to this base and is corrugated, are stacked on each other (for example, Patent Literature 2 and Patent Literature 3). These inventions have excellent features, such as small ventilation losses and low susceptibility to clogging by soot and dust and combustion ash of coal, and are used in great numbers in exhaust gas denitrification devices of thermal power generation boilers.
Also, there have been proposed catalyst structures in which a weir-like protrusion is provided in a flat portion of a catalyst and the occurrence of gas flow boundary layers formed on gas-catalyst surfaces is prevented (for example, Patent Literature 4).
Furthermore, there have been proposed catalyst structures in which gas dispersions made of metal, ceramics or glass are stacked alternately with a plate-like catalyst (for example, Patent Literature 5).